The main finding was that residential SUD patients reported having substantial problems influencing their health-related quality of life as measured using the EQ-5D-3L, with mean index value of.59 at the beginning of treatment, compared to.90 for the general population sample. Where more than half of the general population sample reported no problems on any dimension, only 8.4% of the patients did so. Conversely, more than 30% of the patients reported having at least one dimension with extreme problems, compared to 3.0% of the general population respondents. For comparison to the mean EQ-5D-3L score found in this study, Saarni et al.  reported mean QoL/HRQoL scores based on a sample of Finnish people with various mental health problems, using the EQ-5D-3L and the UK value set (as in this study), including schizophrenia (.715), schizoaffective disorder (.681), major depression with psychotic features (.707), and other psychotic disorders (.639). Our observed mean value for SUD patients is in the same range as Saarni’s reported mean values for other psychotic disorders, and significantly below those reported for e.g. Schizophrenia (p = .0012, not adjusted for differences in e.g. age). More recently, Olesen and colleagues  reported mean EQ-5D-3L values for various chronic conditions in Denmark, the lowest of which were cerebral thrombosis (.621) and angina (.648). They also report decreasing values with increasing number of chronic disorders, such that patients with five or more conditions had a mean EQ-5D-3L value of .597. If we consider somatic patient groups for which substantial studies of QoL have been performed, mean EQ-5D-3L values for cancer patients tend to be reported above .6, and mean EQ VAS between .55 and .8 (See e.g., ). These comparisons should not be interpreted as measures of the relative misfortune of these patient groups, but rather as an indication that the SUD patients in this study report experiencing substantially impaired health and HRQoL. In addition to the heightened mortality of SUD patients, this underlines the importance of identifying successful strategies and treatment options for this patient group.
We also found that the most commonly reported problems were with anxiety/depression, pain/discomfort, and usual activities. Reflecting the comparatively good physical health of the patient group, none of the patients reported being at the worst level on mobility, only one for self-care, and 7 (4%) for usual activities. The responses to the anxiety/depression scale, arguably the most relevant subscale for this patient group, were corroborated by corresponding scores on the HSCL-25, with more than 37% variance explained by the single EQ-5D-3L item. The responses to the EQ VAS were similarly reduced, indicating that the reported health problems were experienced as being detrimental to the patients’ quality of life.
These results suggest that the EQ-5D is sensitive to dimensions of health for which SUD patients experience health problems. Furthermore, the observed reductions in HRQoL implies substantial potential QALY-gains if the patient group were to be successfully treated. In cost/QALY analyses, this would allow for relatively large investments for treatment programs improving the quality of life of SUD patients. However, while observation of reduced QoL at the initiation of treatment suggest that the EQ-5D could be a useful tool in clinical practice, there is call for research investigating the sensitivity of the EQ-5D to changes in the QoL of SUD patients. Additionally, the EQ-5D-3L used in this study uses very wide categories within each dimension, with levels corresponding roughly to “no”, “moderate”, and “extreme” problems. Future research could benefit from the newer EQ-5D-5L, with 5 levels for each dimension, ideally allowing for greater sensitivity to smaller changes in health.
The EQ-5D is a generic instrument, intended to capture broad aspects of health that are of importance to a wide range of patients and conditions, with a minimal number of questions. As such, it is extremely reductionist, covering only 5 dimensions of health, each with a single item. Given this design, the EQ-5D is unlikely to provide a comprehensive description of the symptoms and problems experienced by any particular patient group. More importantly, for certain patient groups, important issues fall outside the scope of the questionnaire. For instance, Saarni and colleagues  report that the EQ-5D values of patients with delusional or bipolar 1 disorders were not statistically significantly different from the general population. If we accept that the QoL of these patient groups is likely to be impaired in reality, this suggests that the EQ-5D does not adequately capture the areas in which these patient groups experience problems. For SUD patients, issues such as stigma and craving might not be fully captured, though both may be partially covered by anxiety/depression and pain/discomfort. Given the brevity of the EQ-5D, it is likely insufficient for clinical monitoring of SUD patients used in isolation. However, this study suggests that the EQ-5D may be suited to capture a wide range of relevant problems experienced by SUD patients, particularly the dimensions anxiety/depression, pain/discomfort, and self-care. As such, the EQ-5D, including the EQ VAS, could potentially form the backbone of a brief, low-cost battery of questions suitable for use in routine monitoring of SUD patients and their symptom.
A longitudinal cohort study found that SUD patients who successfully quit substance use for 1 year showed improved satisfaction with life and reduced psychological distress, compared to SUD patients that relapsed and control participants . The patient population in the Hagen study is similar to the SUD patients described here, and it is reasonable to assume that successful SUD treatment followed by drug abstinence would lead to improved HRQoL, which would hopefully be reflected in EQ-5D values. However, a recommendation to use the EQ-5D in monitoring HRQoL in clinical SUD settings should be considered experimental until the sensitivity to change in this population has been established.
The regression analyses indicate that SUD patients using cocaine report comparatively higher self-reported health and HRQoL than users of other substances. The reasons for this are not apparent, but it is plausible that there are systematic differences between users of different substances in terms of wealth and socio-economic status, with accompanying differences in terms of non-drug-related habits and health, all of which could influence mean reported HRQoL. The analyses also revealed a statistically significant association between phobic anxiety and higher EQ-5D-3L values. Considering that the anxiety/depression dimension is one of the drivers of low EQ-5D-3L values in the SUD sample, this is counterintuitive. However, phobic anxiety is characterized by heightened anxiety levels in response to particular stimuli, which one may hope are not present while undergoing treatment. As such, we may speculate that individuals with phobic anxiety could experience lower anxiety levels while undergoing treatment. Similar effects could be in play for the counter-intuitive statistically non-significant positive point estimates observed for e.g. PTSD and major depression, though these could simply reflect individual variation in responses. Furthermore, the absence of previous diagnoses of e.g. depression could reflect fewer previous contacts with the health care system, rather than better current mental health.
There is a paucity of research on HRQoL and instruments such as the EQ-5D in SUD patients, though a few studies have reported on particular subgroups. Günther and colleagues found that the EQ-5D-3L was less responsive than other tested instruments (GAF, WHOQOL-BREF, and HoNOS) in alcohol dependent patients . van der Zanden and colleagues reported on the suitability of EQ-5D-3L in a sample of 430 patients in Dutch heroin treatment trials, and concluded that the instrument appears suited for this population . Dalen et al. reports on a 2015 study of 365 SUD patients in an outpatient setting in northern Norway, where EQ-5D-3L was included. The results described were limited to proportions of patients reporting problems on mobility (25%, 28.1% in our study), usual activities (49%, 63% in our study), pain/discomfort (68%, 65.2% in our study) and anxiety/depression (60%, 83.1% in our study); and mean EQ VAS score (60, compared to 59.86 in our study) . The reported numbers are strikingly well-aligned, though the sample in our study report somewhat more problems.
One of the major obstacles to successful treatment of SUD patients is drop-out from treatment. Though the rate varies by the definition used to define drop-out, reported rates of 50% are common, and useful methods for prediction and prevention of drop-out are elusive . A research question of potential interest is whether HRQoL can be used to predict drop-out. This requires careful consideration, as it is possible that patients experiencing good quality of life will be less motivated to remain in treatment, meaning that high HRQoL scores could be an indicator of risk. Similarly, low HRQoL scores could be indicative of poor functioning, which could also be a risk factor.
This study is limited in many ways. The patient sample is relatively small, and covers a narrow range of ages, with all participants below the age of 34. Generalizations beyond this age range should be made with care. Similarly, the characteristics of SUD patients could vary between countries and regions, and the problems experienced by SUD patients could vary between societies, health care, and social security systems. Norway is a comparatively wealthy country with low wealth inequality and universal health care, characteristics generally indicative of good population health. Lack of universal health care would be expected to negatively impact the health, and presumably HRQoL, of SUD patients. At the same time, it is possible that failing to meet societal expectations in a country with generally high levels of affluence may result in heightened stigma. Investigations of HRQoL in SUD patients in other countries are called for in order to build a foundation for making generalizations beyond wealthy northern European countries. As noted, the comparatively higher HRQoL reported by users of cocaine remains unexplained, and there may be systematic differences between cocaine users and other SUD patients related to e.g. socio-economic status, markers of which were not included in this study.